having hunted for downed aircraft, including an airliner, and missing ships and stuff; I can tell you that there is a lot of junk floating around on the surface of the ocean that has to be sorted through as you go through a search area. It is a long and meticulous process. We were picking stuff up for six weeks before we were withdrawn from the search effort.
When we shifted from Search-and-Rescue to Search-and-Recovery it was a heart-rending point, as Jug points out. Then the search team is picking up all kinds of junk floating around from who knows where and sorting through it to determine if it came from the aircraft you're looking for or something else.
They did report a seat and an oil slick on the first day, but were unable to recover the seat due to the sea state. Now they can't find it which means its probably sunk. That is a pretty good indication that is where the aircraft crashed, but without being able to recover any debris that clearly came from the aircraft they can't say with absolute certainty.
A lot of speculation and nothing can be ruled in or out. I doubt the terrorism possibility simply because the crash did occur in a major storm system, but no one at this point can rule that out either. So we will see.
I doubt we will ever find out unless by a stroke of extraordinarily good fortune, the black boxes can be located and recovered. At this point all we have is the fragmentary info from the onboard systems received prior to the aircraft breakup and the recorded weather data at the time.
Time will tell.
My prayers are for those lost at sea and their families ashore.